#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int sum(int n)
{
	int i = 0, s = 0;
	while (i<=n)
	{
		i++;
		s += i;
	}
	return s;
}
int main()
{
	int m = 0;
	scanf("%d",& m);
	int ret=sum(m);
	printf("%d", ret);
}